The project is designed to investigate the regulation of glycogen phosphorylase in isolated rat hepatocytes by hormones with particular emphasis on insulin and alpha catecholamines. Alpha catecholamines and vasopressin are thought to activate phosphorylase secondary to an elevation of intracellular calcium. Our interests relate to the nature of the alpha-adrenergic receptors which appear to be of the alpha1 rather than alpha2 category for all metabolic effects of alpha catecholamines. We are interested in the relationship between the increased turnover of phosphatidylinositol seen in hepatocytes after the addition of vasopressin and catecholamines and the elevation of cytosol calcium. There is evidence that phosphatidylinositol turnover is not increased secondary to entry of extracellular calcium. However, the link between these two events remains to be established. We are currently testing the hypothesis that increased turnover of phosphatidylinositol is involved in the primary events which result in the release of bound intracellular calcium and the uptake of extracellular calcium.